Circuit arrangement for automatic resonance tuning of a high-frequency generator, more particularly for the purpose of therapy



G. MARTENS CIRCUIT ARRANGEMENT FOR AUTOMATIC RESONANCE TUNIN OF A HIGH-FREQUENCY GENERATOR, MORE PARTICULARLY FOR THE PURPOSE OF THERAPY Filed Feb. 26, 1952 June 26, 1956 I A T 1 A T I .L

INVENTOR GUNTER I MARTENS KW W7. AGENT United States Patent CIRCUIT ARRANGEMENT FOR AUTOMATIC RESONANCE TUNING OF A HIGH-FREQUEN CY GENERATOR, MORE PARTICULARLY FOR THE PURPOSE OF THERAPY Giinter Martens, Darmstadt, Germany, assignor to Hartford Natioual Bank and Trust Company, Hartford, Conn., as trustee Application February 26, 1952, Serial No. 273,516 Claims priority, application Germany May 22, 1951 3 Claims. (Cl. Hit-36) The present invention relates to a circuit arrangement for resonance tuning of a high-frequency generator. More particularly, the invention relates to a circuit arrangement for automatic resonance tuning of a highfrequency generator, for the purpose of therapy and to improvements in or relating to circuits for automatically maintaining the output circuit of a high-frequency generator in resonance.

It is in the nature of the self-oscillating oscillatory generators which are universally used for short-wave therapy that they are capable of adapting themselves to the loads occurring in the various cases of treatment and to the variations in load occurring upon the unavoidable movements of a patient. This is not possible without variation of the oscillating frequency.

However, in high-frequency generators for medical use the frequency must not greatly differ from a predetermined value, since disturbance in the reception of radio signals may thus be involved.

A generator has been provided for medical use with a crystal-controlled oscillator which is connected to an amplifier. The behavior of such a controlled high-frequency generator with respect to variations in load and more particularly with respect to variations in the natural frequency of the output circuit which always occur in practice is much less supple. It reacts upon such variations by an increased production of heat in the anodes of the oscillatory tubes.

This is dangerous for tubes which are fully loaded in normal operation, so that it has been necessary hitherto to utilize tubes which in normal operation are loaded with a power considerably smaller than that which they can endure and this is naturally not economical.

Furthermore, a device is already known in which the temperature of the final anode is kept under control by means of a photo-electric cell which causes the device to be automatically switched-oil? when the heating becomes excessive. In technical respect this provides a solution of the above-mentioned problem, but leads to undesirable interruption in the treatment of the patient, so that continuous supervision is required to insure that the required amount of radiant energy is administered.

All the aforementioned disadvantages may be overcome by the use of a circuit according to the present invention. By means of this circuit it is possible in highfrequency generators for medical use to tune the circuit of the patient independently to resonance and during treatment to correct any deviation therefrom immediately. This leads to simpler operation, greater reliability and better dosing of the energy administered.

The criterion of the correct adjustment of the circuit of the patient is naturally required to be independent of fluctuations in load. Consequently, it is evident that values such, for example, as current, voltage or power cannot be used for deriving a control value for readjusting the circuit of the patient.

A circuit for a short-wave device for medical use has 2,752,496 Patented June 26, 1955 previously been suggested, by means of which a control value for readjusting a variable condenser included in the circuit of the patient is derived from the deviation from the phase-shift between the voltages in two interconnected resonant circuits tuned to the same frequency, which phase-shift is normally Said circuit may comprise a bridge, of which one branch includes two output resistors and the other is constituted by two discharge tubes operating in the manner of mixing tubes, for example nine element tubes.

According to the invention, in a circuit of this kind, a grid of one of the tubes included in the bridge is connected to the corresponding grid of the other tube, said grids having applied to them an alternating voltage which is derived by way of a capacitative voltage-divider from the primary oscillatory circuit. Furthermore, two other corresponding grids of said tubes are each connected to one extremity of a coil which is centrally connected to ground and which is coupled to the output circuit, and hence to the circuit of the patient in the case of a generator for medical use.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described in greater detail with reference to the accompanying drawing, wherein the figure is a schematic diagram of the circuit arrangement of the present invention.

This circuit comprises a bridge, one branch of which includes two identical resistors 1 and 2. The other branch is constituted by two nine element tubes 3 and 4. The tubes 3 and 4 operate in such manner that a predetermined anode current flows with a phase-shift of 90 between the voltages of the grids 5 and 6 of each tube. The strength of this anode current may be 280 milliarnps. Under these conditions the bridge is in equilibrium, the anodes of the tubes 3 and 4 having the same potential.

The grids 5 are directly connected to one another and acquire alternating voltage which is derived from an anode circuit 7 of an oscillatory tube (not shown) with the use of a capacitative voltage-divider 8. The id 6 of each tube 3 and 4 is connected to one extremity of a coil 9, which is centrally connected to ground. Coil 9 is coupled to the output circuit (patient circuit) 10, which in turn is coupled by inductive means with the primary circuit 7.

The voltages between the ends of coil 9 and the center thereof exhibit a relative phase-shift of and with respect to the voltage on the coil of the primary circuit 7 a phase-shift of +90 and 90 respectively in the event of resonance occurring.

When the circuits become out of resonance, said phase shifts are varied. One phase-shift, for example, becomes +80 and the other l00. In this case the phase difference between the grids 6 and the respective cathodes of the tubes 3 and 4 remains constant. Due to the detuning of the output load circuit the phase-shift on the grids 5 changes with respect to the cathodes. This means that with reference to the alternating voltage waves supplied to the grids 6 of the tubes the alternating voltage on the grid 5 of one of the tubes remains its positive value during a greater part of the half cycle of positive voltage on the grid 6 of this tube and the time the grid 5 of the other tube has a positive value, decreases with respect to the time period the grid 6 of this tube is positive. Consequently, the anode current of one nine element tube increases and that of the other decreases, a difference in potential occurring between the anodes of the tubes 3 and 4. The diflference in potential is used to bring about ignition of either of the thyratrons 11 and 12 according to the polarity. Each anode circuit of the thyratrons includes either of two field windings 13 and 14 of a regulating motor which is coupled, for example through a worm and wormwheel combination, to a varidiverges from the frequency.of the. generator.

"The direction of rotation is dependent upon the field wind- ,ing switched-in and this is determined by the direction in which the natural frequency of thecircuit of the patient In .each case, the direction of rotationofqthe motor is such-that the tuning condenser is moved towards the point of resonance. Said condenser is moved until the position of resonance is reached again. In. thiscas'e. the two thyratrons are inoperative again.

The thyratrons are supplied with alternating voltage. This insures that they immediately become currentless when their grid voltage decreases below the value of the ignition voltage.

It is preferable that the nine element tubes 3. and 4 be. carefully protected from the strong stray field of the generator, since the latter may bring about .disturbance in the operation of said tubes. Consequently, it is desirable that the tubes be arranged within a protective envelope. Furthermore, it is preferable to utilizescreened conductors for the control voltages of the grids Sand 6. Any further conductors entering into the protective envelope willbe led through its wall with the use of blocking condensers. Furthermore, the current supply conductors to the supply sources will be protected from penetration of high-frequency currents by means of low-pass filters such as shown in the lower part of the drawing.

"The point .of ignition of the thyratrons may be adjusted with the use of a potentiometer 16. In order to .be independent of variations in thesupply source voltage, the anode voltage of the tubes 3 and 4 may be stabilized;

variable resistances 17 and 18 serve to adjust the tubes 3 and 4 in the same work-point. A resistor 19 included in the. common cathodelead ofthe two thyratrons prevents the tubes from being ignited simultaneously.

A' condenser 20 is provided to prevent alternating voltage from. being applied to the cathodes of the thyratrons.

IThis voltage would be-highly interfering for the ignition .at theright moment.

tude of the high-frequency .voltages in the oscillatory circuits, sothat even a circuit which-has becomecompletely out of resonance immediately returns to the position of resonance.

It is to .be understood that the invention is not limited to the details disclosed but includes all such variations and modifications as fall Within the spirit of the invention and the scope of the appended claims.

Having thus setforththe nature of. my invention, what :1 claim is:

1. In a system wherein oscillations produced by a generator having a resonant circuit are fed to a load via a tunable output circuit coupled to said resonant circuit, apparatus for maintaining said output circuit in resonance with said resonant circuit comprising a bridge constituted by two parallel branches, one of said branches including a pair of electron discharge tubes each having first and second grids 'and'the other branch including a pair of output resistors-for deriving a control voltage therefrom,

means connected to said resonant circuit to apply. said oscillations produced by said generator to the respective first grids of said tubes, a coil coupled to said .output circuit-and havingits ends connected to the respectivesecond grids of said tubes, the center point of-said coil being grounded whereby the voltage applied to said second grids are in phase opposition, the voltage induced in said coil being displaced substantially ninety degrees relative to said oscillations in said resonant circuit only when said output circuit is in resonance therewith and diverging from ninety degrees when said output circuit departs from resonance to thereby produce in saidbridgethe control voltage depending on theextent of said divergence, means to control the frequency of said tunableoutput circuit, and means to apply said control voltage to said control means to elfect said resonance tuning.

2. ,In a system wherein oscillations produced by agenerator having a resonant circuit are fed to a..load..via a tunable output circuit coupled to .saidresonant circuit, apparatus for maintainingsaid output circuit in resonance with said resonant circuit comprising a bridge. constituted by two parallel. branches, one of said branches including apair of electron discharge tubes each having first and second grids and the other branch including a pairofoutput resistors for deriving control voltages therefrom, means connected to said resonant circuit to apply: said oscillations produced by said generator to the respective first grids of said tubes, a coil coupled to said output circuit and having its ends connected to the respective second grids of said tubes, the center point of said coil being grounded whereby the voltage applied to said second grids are in phase opposition, the voltage induced in said.-.coil being displaced substantially ninety degrees relativeto said oscillations in said resonant circuit only when said output. circuit is in resonance therewith and diverging from ninety degrees when said outputcircuit departs from resonance to thereby produce in said bridge the control voltages depending on the extent of said divergence, a pair of thyratrons each having a cathode, an ignition electrode and an anode, said cathodes being interconnected, a motor for regulating the frequency of said tunable output circuit and including a field winding interconnecting the anodes of said thyratrons, and means to apply .the control voltages produced in said bridge tothe respective ignition electrodes of said thyratrons.

3. Apparatus, as set forth in claim 2, further including a common cathode resistor-for said thyratrons to prevent simultaneous ignition thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,605 Webb NOV. 26, 1946 2,476,849 Ergen July 19,1949 2,478,977 Nicholson Aug. 16, 1949 2,538,539 Stokes Ian. 16,1951 2,611,092 Smullin Sept. 16,1952 

